is stanford’s proposed site safe?

The Alpine Canyon’s heavily vegetated hillsides rise nearly 400 feet up steep slopes from the mouth of the canyon at Alpine Road to the ridgelines above, creating one of the highest fire hazards in Portola Valley according to the Town’s 2009 Fire Hazards Map.  

The extreme fire hazard created by the canyon’s dense vegetation is exacerbated by the canyon’s southeastern exposure and steep slopes.  The southeasterly exposure acts to dry the canyon’s dense vegetation during the long, increasingly hot summer and fall months.  The steep slopes would intensify and accelerate the spread of any fire away from the canyon’s mouth and toward the southwest, the west and the northwest. The simultaneous spread of fire in three different directions above and beyond the ravine would greatly compound and potentially overwhelm the limited resources available to contain and suppress a fire.

The United States Geological Service’s Topographical Map for the Palo Alto Quadrant reveals the perilously steep hillsides ringing the site to the southwest, west, northwest and north:

The closely juxtaposed walls of the ravine are very likely to create a chimney-like effect that intensifies and uplifts the thermal energy of any fire in the canyon, causing pre-heating, uplift and the spread of burning embers from the canyon, possibly in multiple directions simultaneously. Not only would there be little or no time to respond, but there would also be no access for firefighters to interdict the fire before it reached the ridgetops above.  There are no roads or maintained trails into or through the ravine that would allow the access needed to suppress a fire’s leading edge before it reached the ridgetop.

Rapidly climbing the steep canyon slopes, fire emanating in the canyon or its mouth would threaten Stanford’s immediate neighbors along Minoca, Cervantes and Westridge, as well as the hundreds of homes in the interwoven network of ravines and canyons beyond.  The simultaneous spread of fire in different directions above and beyond the ravine toward Minoca Road, toward Cervantes Road, and toward Westridge Drive would greatly increase and could possibly overwhelm the resources needed to contain and suppress a fire originating in the canyon.

Among those resources is water.  Because the ridgelines and surrounding properties are 300 to 500 feet above the mouth of the ravine, pressurized water needed to suppress a fire emanating from the canyon must be drawn from the restricted supply on hand in the water storage tanks along Golden Oak and Goya.  

The map below illustrates the residences and properties within just 1 mile of Stanford’s property that could be put at risk by fire emanating from Stanford’s property.

Fire spreading into any or all of these neighborhoods would quickly intercept and potentially block important access and evacuation routes along Westridge Drive, Cervantes, Minoca and Golden Oak, jeopardizing both fire-fighting and evacuation efforts.  The Town has yet to implement, publicize and rehearse wildfire evacuation procedures, but organizing, communicating and executing such procedures for hundreds of residents with little or no time for advance warning is daunting at best.  Even well-prepared towns with fully implemented and rehearsed evacuation procedures, such as Paradise in 2018, have failed to execute such procedures without grievous loss of life.

Wildfire is not the only danger Stanford’s site presents. The site is traversed by a mapped seismic fault.  Seismic hazards in and around Portola Valley were extensively mapped by the U.S. Geological Survey and others for the National Geologic Map Database of the U.S. Department of the Interior.  T.W. Dibblee, Geologic Map and Sections of the Palo Alto Quadrant (1963).  The portion of Dibblee’s map showing the late quaternary fault that intersects the Alpine Canyon and surrounding area is shown below:

As noted in the General Plan’s Safety Element, “[t]he hazard associated with active fault traces is clear.  Any structure built across such a trace and subsequently offset by faulting would be in danger of collapse and constitute a threat to life.”  In Portola Valley, “a pattern of echelon ground breakage” has occurred, resulting in short ruptures of 40 feet or so oriented obliquely to the general fault trend.  In addition, “a belt of disturbed ground several hundred feet wide or more, characterized by secondary fractures and cracks, ground lurching and warping may develop along traces of dislocation.”

Stanford’s proposed housing site, located at the mouth of the Alpine Canyon watershed, is situated on surficial, unconsolidated alluvial soils.  As the General Plan’s Safety Element notes, such soils present the highest risk of seismically-induced ground shaking, ground settlement and liquefaction, particularly in the immediate vicinity of known fault traces.

The hazard created by the geologic instability of Stanford’s proposed site is not merely seismic.  A seismic event would also increase the risk of fire ignition and spread and disrupt any emergency response to or evacuation from affected areas.

In short, Stanford is proposing to develop 30 residential structures on less than 3 acres of land, creating a highly dense concentration of population and human activity on land that has the least suitable, geologically unstable soils and is located in the highest fire risk setting.  Such perilous proposals are precisely the type of reckless development our General Plan and Municipal Code were designed to prevent.

The dense concentration of structures, people and human activities on such a geologically unstable, high fire risk site is an invitation to disaster.  No matter what engineering justification or statistically based model is presented to downplay the probability of fire ignition or spread within the development, the fact remains that the site proposed for Stanford’s housing project — a fault-ridden geologically unstable alluvium at the mouth of a steep, heavily vegetated canyon with slopes rising 400 feet above the site from the southwest to the north —unquestionably presents an imminent and heightened danger to the surrounding neighbors and beyond.  If fire starts in that location or its immediate vicinity, the result can quickly prove catastrophic.  

The fact also remains that catastrophe and disaster most often result from an unexpected event, an unanticipated mistake, the fluke happenstance that no one considered or fully predicted.  In such circumstances, why jettison the cautionary guidance of our General Plan and ordinances?  Why double-down on the hubris that a set of assumptions applied to recent past experience can accurately serve to guide our expectation of future circumstances, particularly when the climate is changing so rapidly and unpredictably? Why assume that every variable can be anticipated, or that all future circumstances can be foreseen, modeled and controlled?  Does our recent experience with wildfires, pandemic or economic collapse justify such hubris?  No, it does not.

That is why Portola Valley’s General Plan and its Land Use element, Open Space element, Conservation element, Alpine Corridor Plan, Safety element and even the Housing element (when read and applied properly) wisely spell out and underscore the reasons to maintain Stanford’s land in undeveloped, open space and the wisdom of doing so.

The General Plan 

Repeatedly and unambiguously, the General Plan cautions against the development of housing in settings as perilous and yet as vital as Stanford’s proposed site.  Among the Plan’s Major Community Goals, the fourth community goal is 

“to guide the location, design and construction of all developments so as to … reduce the exposure of people and improvements to physical hazards such as earthquakes, landslides, fire, floods, traffic accidents and to provide evacuation routes for emergencies.”  General Plan Introduction 

Land Use Element  

The Land Use Element specifically directs the Town’s planners and officials “to ensure that development in areas subject to geologic, fire and flooding hazards is controlled so that people and structures are not exposed to unacceptable levels of risk.”  

“In any development within the planning area, full consideration should be given to the geologic conditions so that development on unstable land can be avoided or minimized.”

“In all developments in the planning area, full consideration should be given to fire protection needs, including those identified in the safety element, and adequate measures should be taken to ensure that these needs are met.” 

“Development should be limited in areas when fire risk cannot be reduced to an acceptable level and adequate emergency access cannot be provided.  Also, recognizing fire protection measures could have adverse effects on native vegetation, development should be configured to minimize damage as well as fire hazard.”

Given the hazards that such perilous sites create, the Land Use element warns that population densities “should be guided by considerations of topography, geology, vegetative cover, access to transportation and services, fire hazards, emergency access, impact on preexisting residential development and other factors.”  In particular, “steep slopes, potentially unstable ground, canyons and ravines should be left undisturbed as residential open space preserves.”

Stanford’s proposed site for a high-density housing project contravenes each of these principles.  The site is situated on unstable soils traversed by a geologic fault at the mouth of a vital watershed whose creek-bed is ringed from the southwest to the northwest by steep, heavily vegetated hillsides with slopes in excess of 30%.  The land should be kept free of structures, especially such dense and numerous housing structures as Stanford proposes, and left instead in its natural condition for the protection and benefit of the wildlife that inhabit and depend on it. 

Open Space Element

The Open Space Element identifies two important Town policies for maintaining the Alpine Canyon watershed as an undeveloped open space:  the protection of public health and safety by precluding development on lands subject to such hazardous conditions as earthquake fault zones, unstable soils, lands with high fire risks and watersheds, and the preservation of the town’s unique natural habitat and resources.

The town’s policies and decisions should “preserve as open space, insofar as necessary, those areas subject to inherent natural hazards in order to ensure the public safety and welfare.”   In particular, “areas hazardous to the public safety and welfare should be retained as open space,” including “slopes generally over 30 percent, fault zones — bands on either side of known fault traces sufficient to include lands of probable ground rupture, areas of geologic instability and streams and their flood plains.”

In fulfilment of these policies, the General Plan’s Comprehensive Plan Diagram specifically designates Stanford’s property as a Residential Open Space Preserve which, according to the Open Space Element, should be “kept as open space because of environmental constraints such as steep terrain, unstable land, and sensitive habitat.”

Conservation Element  

The Conservation Element would limit and, where necessary for public safety, prohibit development in hazardous geologic areas.  Like the Open Space Element, the Conservation Element relies on the enactment and enforcement of appropriate Town regulations to protect the health and safety of the community.  

“The regulations should include control over development in areas where natural hazards exist.  These regulations will achieve the objectives with careful and imaginative guidance by town staff, elected representatives and citizens.”

Safety Element  

The Safety Element is intended to prevent loss of life, to reduce injuries and property damage, and to minimize economic and social dislocation that may result from earthquakes, other geologic hazards, fires and flooding.  It seeks “to increase public awareness of geologic, fire and flooding hazards, and of available ways to avoid or mitigate the effects of these hazards.”  By attempting to define the relative degree of risk in various parts of town, it strives to provide a sound basis for designating land uses that are appropriate to the geologic, fire and flooding risks of a proposed development site, and thereby “minimize the risk to human life from structures located in hazardous areas.”

The Safety Element was written and adopted in 2010 before we experienced the catastrophic wildfires that have plagued California since 2015, the increasingly deleterious effects of climate change, or the devastating coronavirus pandemic of 2020.  It is in urgent need of revision and updating in light of lessons learned from each of these calamities.

In particular, the Safety Element does not incorporate many of the lessons learned since 2010 from California’s recent experience with catastrophic wildfires.  It does not assess the topographic, climatic, seasonal and weather conditions that can accelerate and exacerbate the rapid spread of wildfire throughout a community, nor does it assess the way in which unsound land use policy and/or development can threaten the lives and property of neighboring property owners.  And finally, it does not consider how seismic events can cause and contribute to the rapid, uncontrolled proliferation and spread of fire.

The Safety Element catalogs a variety of potential hazards, such as faulting, soil shaking, liquefaction, flooding, soil expansion and fire, and then generally assesses their respective degrees of risk in various areas of town.

With respect to seismic faulting, the Safety Element states that the most detailed information regarding the description and location of the most recognizable active fault traces in Portola Valley is contained in the unpublished W.R. Dickinson, “Commentary and Reconnaissance Photogeologic Map of the San Andreas Rift Belt, Portola Valley, California.”   Unfortunately, the Safety Element does not publish Dickinson’s map and it is not available on the Town’s website or the Internet.

As noted above, the U.S. Geological Survey’s map of the town for the National Geologic Map Database (T.W. Dibblee, Geologic Map and Sections of the Palo Alto Quadrant (1963)) identifies an extensive fault between Jasper Ridge and Felt Lake crossing Westridge Drive and the Stanford Wedge.  In addition to the plan view depiction presented above, Dibblee’s map provides a series of subsurface cross-sections showing the fault’s angle and depth as well as the subsurface soils surrounding the fault to the northwest (cross-section B) and to the southeast of Stanford’s property (cross-section C).

Stanford’s proposed housing site sits on an alluvium at the mouth of a steep creek-fed ravine situated between these two cross-sections.  As the relevant portion of the Town’s Geologic Map shows below, the soils underlying Stanford’s proposed housing site are surficial, unconsolidated alluvium deposits subject to the highest risk of ground shaking:

Such unconsolidated soils also present an increased risk of ground settlement and liquefaction in the event of an earthquake.  According to the Safety Element, “[s]eismically induced ground settlement or ‘shakedown’ may occur very rapidly” and — particularly when aggravated by human or seismic processes — “may be unequally distributed over a small area with damaging effects to foundations or structures resting directly on the settled ground.”

Soil liquefaction occurs when unconsolidated water-saturated soils, subjected to intense shaking, temporarily lose their tensile strength and instead behave like a fluid.  “Soils most susceptible to liquefaction are saturated, well-sorted, poorly compacted fine sands and silts.”  The risk of liquefaction in localized areas along valley floors underlain by unconsolidated alluvium and a seasonally high-water table is considered relatively high.  The California Geological Service’s Seismic Hazard Zones has mapped the areas of potential liquefaction beneath and surrounding Stanford’s proposed housing site:

The green shaded area depicts areas “where historical occurrence of liquefaction, or local geological, geotechnical and ground water condition indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693 (C) would be required.”  Although State law thus mandates further geologic investigation of Stanford’s proposed site prior to any development of the site, Stanford’s current submission and Tentative Map provide no geological investigation of the site, the fault crossing the site or its subsurface and surrounding soils.

Because Stanford’s proposed site sits at the mouth of the Alpine Canyon, it is also highly susceptible to significant erosion and sedimentation.  As the Safety Element notes, “[e]rosion occurs chiefly on steeper slopes in the upper reaches of drainage basins where runoff velocities are high.  Sedimentation, on the other hand, takes place mainly in the lower reaches of drainages where stream gradients and velocities are reduced.”  Although the Town has performed no detailed study, the Safety Element states that “surficial deposits of alluvium and slope wash as well as landslide deposits can be expected to be most susceptible to erosion.”

Finally, based on the Fire Hazards Map prepared for the Town in 2009 by Moritz Arboricultural Consultants, Stanford’s land in the Alpine Canyon is among the highest fire risk hazards in town.

As the Safety Element concludes:

“Several steep wooded canyons and steep slopes … are classified as the ‘highest’ risk.  These canyons are generally the steep back portions of lots where homes, often with wood roofs, are located higher on the properties.  Fires in these somewhat remote areas pose a major threat and warrant coordinated actions by property owners bordering the canyons.”

The Moritz classification of Stanford’s site as among the highest fire risk hazards in town was based solely on the profusion of dense vegetation throughout the site. Significantly it did not address or consider how the topography of the site, its geologic instability, its southeasterly exposure or its setting relative to neighboring lands and properties would compound and exacerbate the hazard presented by the site. 

But, as the Safety Element pointedly notes, actual fire hazard is dependent on many factors in addition to vegetation, including water supply, accessibility, land slope and flammability of structures.  “Land slope,” it notes, “influences fire safety in two ways.  First, fire spreads up steep slopes far faster than it does on level land.  Secondly, the slope of the land determines how easy it is to move firefighters and equipment to the scene of the fire or other emergencies.”

Housing Element

The 2014 Housing Element amendment purports to examine the suitability of a number of alternative housing development sites in town with reference to their geologic and fire risk constraints:   

“Portola Valley faces different constraints on development than any other community on the Peninsula, with the possible exception of Woodside, much of Portola Valley is unsuitable for development for one or more reasons.  The major constraints on development are the presence of the San Andreas fault, large areas of landslides, the steepness of slopes, and the fire hazards due to natural conditions.”

Although the 2014 Housing amendment professes concern for the selection of safe development sites in Portola Valley’s physically risky and challenging setting, in practice it simply ignores the serious safety issues with Stanford’s proposed housing site.  In calling for the development of 27 single family dwellings on Stanford’s property in the Alpine Canyon, it simply ignores and dismisses the long-held and carefully-crafted policies, principles and standards set forth in our General Plan and Municipal Code for safe land use, protection of open space and wildlife habitat, conservation of natural resources and recreation that disfavor such dense housing in such perilous and environmentally sensitive settings.    

After a lengthy discussion of alternative development projects, the 2014 amendment zeros in on Stanford’s property in the Alpine Canyon as a potential site for dense housing development.  It does so, however, with no consideration or acknowledgment whatsoever of the severe seismic, ground shaking, liquefaction, or fire risks of the site.  Nor does it address or consider the long-standing land use, open space, conservation, recreational and scenic policies that discourage and oppose development of the site.

Inexplicably, nowhere does the 2014 Housing Element amendment refer to or mention its own depiction in Exhibit 1 of the fault running through Stanford’s proposed housing site:

Nor does the 2014 amendment refer to or describe the proposed housing site’s severe risk of liquefaction depicted in its own Exhibit 2:

 Or the fact that the Town’s expert consultant classified Stanford’s proposed housing site as among the highest fire risks in Town, as the amendment’s own Exhibit 4 clearly shows:

Informed consideration of any of these four factors — let alone all of them combined — would exclude Stanford’s property in the Alpine Canyon from consideration under our General Plan and Municipal Code for development of a subdivision, residential planned unit development or multifamily housing project.